This invention concerns a process for the removal and optional recovery of sulfur oxides from gaseous streams using a solid resin adsorbent. More particularly the invention concerns the treatment of waste streams such as stack gases discharged from generating plants, industrial plants which produce sulfur derivatives and other facilities that burn sulfur-containing coal or oil.
As a result of the enactment of the recent Federal Clean Air Act and corresponding state legislation designed to provide for the implementation of standards approved by the Federal Environmental Protection Agency, a major portion of the fossil-fueled power plants in the U.S. are under order to reduce their output of sulfur dioxide substantially in the near future. Some of these emission standards may be attained by the use of low sulfur fuels, but sufficient supplies of such fuels for all generating units will not be available for many years.
At present no acceptable method to adsorb sulfur oxides from hot gaseous streams appears known which would comply with today's stringent environmental standards. The art does disclose a wet scrubbing process which provides for the gaseous stream to be contacted with lime/limestone slurries to form insoluble calcium solids. Unfortunately no practical method has been developed for the disposal of this quicksand-like sludge. Furthermore the disposal of these wastes has caused concern to environmentalists.
The prior art further contains various suggestions for removing sulfur dioxide from gases utilizing resins. See, for example, U.S. Pat. Nos. 3,709,977; 3,727,379 and French Pat. No. 1,356,116. None of these resins however perform satisfactorily over broad ranges of temperatures and resin moisture conditions. They are particularly deficient in the case of stack gas purification.
The inadequacy of the prior art resins has been theorized to be related to the marked decrease in capacity such resins experience at low moisture levels. When a wet solid adsorbent is contacted with, for example, a hot stack gas, a substantial drying of the adsorbent takes place despite the presence of moisture in the gas. Such dehydration renders many resins ineffective particularly if the moisture content falls much below the 50% mark. Consequently the utilization of such resins requires the cooling of such stack gases usually to temperatures circa 50.degree.C. to avoid dehydration of the resinous adsorbents and followed by significant reheating of the gases to provide buoyancy for the gases to escape from tall stacks.
It is a primary object of the present invention to provide a process for removing sulfur oxides over a broad range of temperature and moisture conditions.
It is additionally an object of the present invention to prevent air pollution due to sulfur dioxide emission.
It is a further object of the present invention to provide a process which will allow industrial sulfur dioxide emissions to meet governmental standards.
Another object is to provide a sulfur oxide recovery process which will produce saleable sulfur products including, for example, elemental sulfur, sulfuric acid, sulfur dioxide, sodium sulfate and sodium bisulfate.
A further object of the invention is to provide a method of recovery of sulfur oxides from stack gases.
These and other objects are achieved by the present invention set forth now in greater detail.